Genetically-modified mice provide a tractable approach to test the biological significance of protein function in complex processes such as thrombosis and leukocyte extravasation. Core A will serve as a mouse genetics core facility to provide advice, training, and services to project investigators in the design and implementation of mouse gene targeting and transgenesis projects including ES cell culture, transfection and screening for homologous recombination, blastocyst injection, and characterization of germline transmitted alleles in founder lines. In addition. Core A will provide project investigators with access to a library of mice maintained by the Core including Cre expressing lines for conditional deletion or overexpression of proteins in vascular cells (platelets, endothelial cells, smooth muscle cells, several types of leukocytes).